introduction to algorithms and data structuresmap/1051/s14/01intro.pdf · 2014-01-13 · analog vs....
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CSC 1051 – Algorithms and Data Structures I
Dr. Mary-Angela Papalaskari Department of Computing Sciences Villanova University
Course website: www.csc.villanova.edu/~map/1051/ Some slides in this presentation are adapted from the slides accompanying Java Software Solutions by Lewis & Loftus
CSC 1051 M.A. Papalaskari, Villanova University
Introduction to Algorithms and Data Structures
What is this course about?
• Computer Science • Problem solving • Algorithmic thinking • Data representation • Software engineering
CSC 1051 M.A. Papalaskari, Villanova University
Our textbook
Java Software Solutions Foundations of Program Design
Seventh Edition
John Lewis William Loftus
Course website www.csc.villanova.edu/~map/1051/ Links to: • Schedule - meetings, slides, projects, labs, etc. • Syllabus - course information • Piazza - class discussions, announcements • Blackboard - homework exercises, submit
projects, check grades
CSC 1051 M.A. Papalaskari, Villanova University
An old quote A priest asked: “What is Fate, Master?” And he answered: “It is that which gives a beast of burden its reason for existence. It is that which men in former times had to bear upon their backs. It is that which has caused nations to build byways from City to City upon which carts and coaches pass, and alongside which inns have come to be built to stave off Hunger, Thirst and Weariness.” “And that is Fate?” said the priest. “Fate... I thought you said Freight,” responded the Master. “That's all right,” said the priest. “I wanted to know what Freight was too.”
- Kehlog Albran Source unknown. This quote appeared as one of the “fortunes” displayed by the fortune cookie program on old unix systems. (“fortune” was a program that ran automatically every time you logged out of a unix session and displayed a random, pithy saying.)
CSC 1051 M.A. Papalaskari, Villanova University
Reverse History of computing Examine what we already know, travel backwards… 1. What we see now all around us – a connected
world of computing
2. Focus on a single “traditional” computer
3. Dig deeper – data and processing
CSC 1051 M.A. Papalaskari, Villanova University
Networks A network is two or more computers
that are connected so that data and resources can be shared
CSC 1051 M.A. Papalaskari, Villanova University
A Local-Area Network (LAN) covers a small distance and a small number of computers
A Wide-Area Network (WAN) connects two or more LANs, often over long distances
The Internet History: Started as a United States government project, sponsored by the Advanced Research Projects Agency (ARPA) in late 1960’s See also: http://www.internethalloffame.org/internet-history/timeline
• 1970’s and 1980’s: ARPANET – wide area network
– protocols for communication
• 1990’s: World Wide Web – html and web browsers
CSC 1051 M.A. Papalaskari, Villanova University
Image source: http://www.computerhistory.org/internet_history/full_size_images/1969_4-node_map.gif
1969: first four nodes of the internet
The Arpanet in 1971
CSC 1051 M.A. Papalaskari, Villanova University
‘Interface Message Processor’ (IMP) evolved into today’s routers.
Image source: http://www.computerhistory.org/internet_history/index.html
The World Wide Web The Internet Protocol (IP) determines how data are routed across network boundaries.
Each computer on the Internet has a unique IP address, such as: 204.192.116.2
Data are accessed using a Uniform Resource Locator (URL): eg: http://www.cnn.com ftp://java.sun.com/applets/animation.zip
• A URL specifies a protocol (http), a domain, and possibly specific documents
• Web documents are often defined using the HyperText Markup Language (HTML)
CSC 1051 M.A. Papalaskari, Villanova University
The World Wide Web • The World Wide Web allows many different types of
information to be accessed using a common interface
• Resources presented include: – text, graphics, video, sound, audio, executable programs
• A browser is a program which accesses network resources and presents them – Popular browsers: Chrome, Internet Explorer, Safari, Firefox
– My first browser: Mosaic <3
CSC 1051 M.A. Papalaskari, Villanova University
Reverse History of computing Examine what we already know, travel backwards… 1. What we see now all around us – a connected
world of computing
2. Focus on a single “traditional” computer
3. Dig deeper – data and processing
CSC 1051 M.A. Papalaskari, Villanova University
A Computer Specification
• Consider the following specification for a personal computer: – 3.07 GHz Intel Core i7 processor – 4 GB RAM – 750 GB Hard Disk – 16x Blu-ray / HD DVD-ROM & 16x DVD+R DVD
Burner – 17” Flat Screen Video Display with 1280 x 1024
resolution – Network Card
CSC 1051 M.A. Papalaskari, Villanova University
Computer Architecture
CSC 1051 M.A. Papalaskari, Villanova University
Memory
Main memory is divided into many memory locations (or cells)
9278 9279 9280 9281 9282 9283 9284 9285 9286
Each memory cell has a numeric address, which uniquely identifies it
CSC 1051 M.A. Papalaskari, Villanova University
Why is main memory called “RAM”????
CSC 1051 M.A. Papalaskari, Villanova University
“Random Access Memory (RAM)”
9278 9279 9280 9281 9282 9283 9284 9285 9286
10011010 You don’t have to scan the memory sequentially – go to data directly using the address
CSC 1051 M.A. Papalaskari, Villanova University
What is “ROM”? is it the opposite of “RAM”????
CSC 1051 M.A. Papalaskari, Villanova University
What is “ROM”? is it the opposite of “RAM”????
CSC 1051 M.A. Papalaskari, Villanova University
Read Only Memory
What is “ROM”? is it the opposite of “RAM”????
CSC 1051 M.A. Papalaskari, Villanova University
Read Only Memory
NO! ROM is also
random access
RAM vs. ROM • RAM - Random Access
Memory
synonymous with main memory:
• fast
• read/write
• volatile
• random access
• ROM - Read-Only Memory
ROM typically holds the firmware, eg BIOS
• fast (except in CD-ROM)
• read only
• non-volatile
• random access
CSC 1051 M.A. Papalaskari, Villanova University
CPU and Main Memory
Central Processing
Unit
Main Memory
Chip that executes program commands
Primary storage area for programs and data
that are in active use
Synonymous with RAM
CSC 1051 M.A. Papalaskari, Villanova University
CPU and Main Memory
Central Processing
Unit
Main Memory
Chip that executes program commands
Primary storage area for programs and data
that are in active use
Synonymous with RAM
Historic note: Von Neuman architecture John Von Neuman, USA 1945
CSC 1051 M.A. Papalaskari, Villanova University
Von Neumann in the 1940s http://en.wikipedia.org/wiki/Von_Neumann
The Central Processing Unit • A CPU is on a chip called a microprocessor
• It continuously follows the fetch-decode-execute cycle:
fetch
Retrieve an instruction from main memory
decode
Determine what the instruction is
execute
Carry out the instruction
CSC 1051 M.A. Papalaskari, Villanova University
The Central Processing Unit • A CPU is on a chip called a microprocessor
• It continuously follows the fetch-decode-execute cycle:
fetch
Retrieve an instruction from main memory
decode
Determine what the instruction is
execute
Carry out the instruction
system clock controls speed, measured in gigahertz (GHz)
CSC 1051 M.A. Papalaskari, Villanova University
The Central Processing Unit
Arithmetic / Logic Unit
Registers
Control Unit
Small, very fast memory
Performs calculations and makes decisions
Coordinates processing (system clock, decoding, etc)
CSC 1051 M.A. Papalaskari, Villanova University
Historic Notes: Automatic control of computation
• The concept of a machine that can follow a series of steps - a “program”
• Some early steps: – Jacquard loom (France 1801) – Babbage's Difference engine and Analytical engine
(England 1822) – Holerith's census machine (USA 1890)
• Colossus Mark I – first electronic computer to be programmable (Alan Turing, England 1944)
• Stored program and the fetch/decode/execute cycle (John von Neumann, USA 1945)
• ENIAC - first fully electronic digital computer (Eckert and Mauchley, University of Pennsylvania, 1946)
CSC 1051 M.A. Papalaskari, Villanova University
Jacquard Loom
CSC 1051 M.A. Papalaskari, Villanova University
punched cards determine the pattern
This portrait of Jacquard was woven in silk on a Jacquard loom and required 24,000 punched cards to create (1839). It was only produced to order. Charles Babbage owned one of these portraits; it inspired him in using punched cards in his analytical engine. Collection of the Science Museum in London, England. (Source: Wikipedia)
Charles Babbage & Ada Lovelace
CSC 1051 M.A. Papalaskari, Villanova University
Designed the Analytical Engine First “Programmer” for (not yet built) Analytical Engine
1945: The word “computer” changes its meaning
CSC 1051 M.A. Papalaskari, Villanova University
Captain Grace Hopper and other computers
The Electronic Numeric Integrator and Calculator (ENIAC) Programmers Betty Jean Jennings (left) and Fran Bilas (right) operate ENIAC's main control panel at the Moore School of Electrical Engineering. (U.S. Army photo from the archives of the ARL Technical Library)
Reverse History of computing Examine what we already know, travel backwards… 1. What we see now all around us – a connected
world of computing
2. Focus on a single “traditional” computer
3. Dig deeper – data and processing
CSC 1051 M.A. Papalaskari, Villanova University
Data Representation • Computers store all
information digitally, using binary codes:
– numbers – text – images – audio – video – program instructions
CSC 1051 M.A. Papalaskari, Villanova University
9278 9279 9280 9281 9282 9283 9284 9285 9286
01110100
Analog vs. Digital Data • Analog
– continuous, in direct proportion to the data represented – music on a record album - a needle rides on ridges in the grooves
that are directly proportional to the voltages sent to the speaker
• Digital – information is broken down into pieces, and each piece is
represented separately – sampling – record discrete values of the analog representation
CSC 1051 M.A. Papalaskari, Villanova University
Binary Numbers • Number system consisting of 1’s & 0’s
• Simplest way to represent digital information: – Electronic circuits: high/low voltage – Magnetic devices (eg hard drive): positive/negative – Optical devices (eg DVD): light reflected/not
reflected due to microscopic grooves
A binary digit is called a bit - binary digit
CSC 1051 M.A. Papalaskari, Villanova University
A byte is a group of eight bits
01110100 • a number? • a letter? • the red component of a pixel? • a program instruction?
CSC 1051 M.A. Papalaskari, Villanova University
Computing devices store use binary codes to reprepresent data of all kinds
Example: Representing Text • Characters, including spaces, digits, and
punctuation are represented by numeric codes
CSC 1051 M.A. Papalaskari, Villanova University
The Unicode character set extends ASCII to sixteen bits per character, allowing for 65,536 unique characters.
The ASCII (American Standard Code for Information Interchange) character set uses eight bits per character, allowing for 256 unique characters
H i , H e a t h e r .
72 105 44 32 72 101 97 116 104 101 114 46
01110100 ASCII
00000000 01110100 UNICODE
CSC 1051 M.A. Papalaskari, Villanova University
Example: Representing Pixels
Color 116, 86, 142)
red=116 green=86 blue=142
Example: Representing Program Instructions
01110100
Intel opcode for the instruction JZ (jump if zero):
CSC 1051 M.A. Papalaskari, Villanova University
Historic note: Trends that gave rise to the modern computer • Mechanization of arithmetic – the concepts of
numbers, symbols, algorithms, and computation
• Automatic control of computation – a “program” to control operations (fetch/decode/execute cycle and the stored program concept)
CSC 1051 M.A. Papalaskari, Villanova University
+
= modern computer
Basic human needs: counting & measuring
CSC 1051 M.A. Papalaskari, Villanova University
http://ghoststudy.com/new11_galleries/halloweve1067.jpg
http://www.dreamstime.com/royalty-free-stock-photography-counting-sheep-image129737
Historic Note: Mechanization of arithmetic • Development of number systems
– Abacus (2400 BC) – Number systems (Babylonian, Greek, Roman, Arabic
1000 BC - 800 AD) • The notion of an algorithm
– Euclid (300 BC) – al-Khwārizmī (780 AD)
• Creation of special purpose calculators – Stonehenge (1900-1600 BC) – Napier's bones (1600, a precursor of the slide rule) – Pascal's adder (1642) – Leibniz's calculator (1670s) – modern calculators
CSC 1051 M.A. Papalaskari, Villanova University
Computer Science A new paradigm in humanity’s search for understanding of: • Representation & encoding • Computation • Problem solving • Mechanization History Epilogue: Just like Physics and other sciences branched off from philosophy during the Renaissance, so CS emerged in the 20th century from the work of philosophers and mathematicians – with the help of dedicated, visionary practitioners, experimental scientists and engineers.
CSC 1051 M.A. Papalaskari, Villanova University
Mechanization of arithmetic – the concepts of numbers, symbols, algorithms, and computation Automatic control of computation – a “program” to control operations (fetch/decode/execute cycle and the stored program concept)
+
= modern computer
Part 2 – introduction to Java
CSC 1051 M.A. Papalaskari, Villanova University
• Programmer writes Source code • Translation produces the binary equivalent –
Object code • Translation is performed by an assembler,
compiler, or interpreter (stay tuned)
CSC 1051 M.A. Papalaskari, Villanova University
High-level programming languages
Java Translation
Java source code
Machine code
Java bytecode
Bytecode interpreter
Bytecode compiler
Java compiler
CSC 1051 M.A. Papalaskari, Villanova University
Development Environments • There are many programs that support the
development of Java software, including: – Sun Java Development Kit (JDK) – Sun NetBeans – IBM Eclipse – IntelliJ IDEA – Oracle JDeveloper – BlueJ – jGRASP
• Though the details of these environments differ, the basic compilation and execution process is essentially the same
CSC 1051 M.A. Papalaskari, Villanova University
Java Program Structure • In the Java programming language:
– A program is made up of one or more classes – A class contains one or more methods – A method contains program statements
• These terms will be explored in detail throughout the course
• A Java application always contains a method called main
• See Lincoln.java
CSC 1051 M.A. Papalaskari, Villanova University
CSC 1051 M.A. Papalaskari, Villanova University
//******************************************************************** // Lincoln.java Author: Lewis/Loftus // // Demonstrates the basic structure of a Java application. //******************************************************************** public class Lincoln { //----------------------------------------------------------------- // Prints a presidential quote. //----------------------------------------------------------------- public static void main (String[] args) { System.out.println ("A quote by Abraham Lincoln:"); System.out.println ("Whatever you are, be a good one."); } }
Java Program Example
Java Program Structure
public class MyProgram { }
// comments about the class
class header
class body
Comments can be placed almost anywhere
CSC 1051 M.A. Papalaskari, Villanova University
Java Program Structure
public class MyProgram { }
// comments about the class
public static void main (String[] args)
{ }
// comments about the method
method header method body
CSC 1051 M.A. Papalaskari, Villanova University
Comments • Comments in a program are called inline
documentation
• They should be included to explain the purpose of the program and describe processing steps
• They do not affect how a program works
• Java comments can take three forms: // Basic this comment runs to the end of the line
/* Basic this comment runs to the terminating symbol, even across line breaks */
/** this is a javadoc comment */
CSC 1051 M.A. Papalaskari, Villanova University
Identifiers • Identifiers are the words a programmer uses in a
program
• An identifier can be made up of letters, digits, the underscore character ( _ ), and the dollar sign
• Identifiers cannot begin with a digit
• Java is case sensitive - Total, total, and TOTAL are different identifiers
• By convention, programmers use different case styles for different types of identifiers, such as – title case for class names - Lincoln
– upper case for constants - MAXIMUM CSC 1051 M.A. Papalaskari, Villanova University
Identifiers • Sometimes we choose identifiers ourselves when
writing a program (such as Lincoln)
• Sometimes we are using another programmer's code, so we use the identifiers that he or she chose (such as println)
• Often we use special identifiers called reserved words that already have a predefined meaning in the language
• A reserved word cannot be used in any other way
CSC 1051 M.A. Papalaskari, Villanova University
Reserved Words
• The Java reserved words:
abstract assert boolean break byte case catch char class const continue default do double
else enum extends false final finally float for goto if implements import instanceof int
interface long native new null package private protected public return short static strictfp super
switch synchronized this throw throws transient true try void volatile while
CSC 1051 M.A. Papalaskari, Villanova University
White Space (Spaces, blank lines, and tabs )
• Extra white space is ignored
• Programs should be formatted to enhance readability, using consistent indentation
• See Lincoln2.java, Lincoln3.java
CSC 1051 M.A. Papalaskari, Villanova University
Errors
CSC 1051 M.A. Papalaskari, Villanova University
Errors • A program can have three types of errors
• The compiler will find syntax errors and other basic problems (compile-time errors)
– If compile-time errors exist, an executable version of the program is not created
• A problem can occur during program execution, such as trying to divide by zero, which causes a program to terminate abnormally (run-time errors)
• A program may run, but produce incorrect results, perhaps using an incorrect formula (logical errors)
CSC 1051 M.A. Papalaskari, Villanova University
The original ”bug” found in the relays of Harvard’s Mark II computer by Admiral Grace Murray Hopper’s team.
CSC 1051 M.A. Papalaskari, Villanova University Source: en.wikipedia.org/wiki/File:H96566k.jpg
Summary • History of computing
• Computer hardware and software overview
• An introduction to Java: – a first program
– identifiers
– comments
– bugs
CSC 1051 M.A. Papalaskari, Villanova University
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